2018-01-16_REPORT - M1977004

• Permit No: M1977004
• IBM Index Class Name: REPORT
• Doc Date: 1/16/2018
• Doc Name Note: Reclamation Report
• From: Homestake Pitch Project
• To: DRMS
• Email Name: DMC
• Media Type: D
• Archive: No

r
Homestake Mining Company 2017 Geotechnical Observations
rPitch Reclamation Project Indian and Tie Camp Rock Dumps
Homestake Pitch Reclamation Project
Annual Geotechnical Report(M-1977-004HR)
' 2017 Geotechnical Observations
Indian and Tie Camp Rock Dumps
1. Indian Creek Rock Dump
The following summary provides a description of the Indian Rock Dump water levels for
' 2017. The Indian Rock Dump is a generally south-facing, graded and reclaimed rock dump
that can be separated into bench levels corresponding to ground surface elevation. The
Indian Rock Dump was regraded in 1994 following procedures approved by the Division
r under Technical Revision#1 in February 1994. In 1995, several minor, localized areas of
slope instability were noted, corrected, and reported in the 1995 Annual Geotechnical
Report(HMC 1996). No significant changes in surface ground conditions were noted in
2017. Subsurface water is monitored in piezometers at the levels described below(Figure
2)
"10300— 10100" Level
rSite Description: Identical to that of past reports for 1996 through 2016.
2017 Observations: Field observations indicate that the repairs performed in 1995 were
' successful and no new areas of surficial instability were observed from 1996 through 2017.
Piezometer 1030OR is located in the central portion of the Indian Rock Dump and monitors
subsurface water levels (Figure 2) In 2011, Piezometer IC10300 was replaced due to
sediment buildup in the casing making it difficult to measure the rise in the water level. It
was abandoned and replaced by Piezometer IC10300R, located approximately 30 feet west
of Piezometer IC10300. Piezometer IC1030OR appears to intersect the east branch of
Indian drainage (under the Indian Rock Dump)just north of the confluence with the west
' branch. In 2017, the water level in Piezometer 1030OR increased during the spring freshet
by 8.9 feet, compared to 7.21 feet in 2016. In 2014, a year characterized by comparatively
heavy snow pack, the water level in Piezometer IC1030OR rose by 17.9 feet. Following the
' spring freshet of each year the water level approaches steady-state levels. The 1030OR well
is in an area affected by the 2017 in situ source zone treatment program. As such, short-
term water levels fluctuated in response to these activities, but returned to steady-state
levels later in the fall (Figure 5).
,/
10400-10370 Level
r Site Description: In 1997 the face of the permanent low-grade stockpile was reconstructed
on the Indian Rock Dump to reduce the potential for infiltration and promote more rapid
runoff from the stockpile area.
r 2017 Observations: In 2011, Piezometer IC10370 was replaced by Piezometer IC10370R,
on the 10,370 level of the Indian Rock Dump (Figure 2). Piezometer IC1037OR is
approximately 67 feet west of the Piezometer IC10370 location, which appears to intersect
' the west branch of Indian drainage below the Indian Rock Dump just north of the confluence
with the east branch. The water level in Piezometer IC1037OR rose by 5.2 feet in 2017 in
response to spring snow melt, similar to the near 6-foot water level increases observed in
Pitch Reclamation Project Page 3
2017 Annual Geotechnical Report
M-1977-004HR
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